Catalyst

ABSTRACT

The present invention provides a catalyst containing titanium in bonded form, non-crystalline silicon dioxide and at least one crystalline silicate phase which has a zeolite structure, wherein the non-crystalline silicon dioxide is applied to at least one of the crystalline silicate phases which have a zeolite structure and wherein at least one of the crystalline silicate phases which have a zeolite structure contains silicon-carbon bonds with which non-hydrolytically separable organic groups R are bonded to silicon. Furthermore, the present invention provides a process for preparing this catalyst and a process for producing an epoxide from a compound which contains a carbon-carbon double bond (preferably from propene) comprising reacting the compound which contains a carbon-carbon double bond with hydrogen peroxide in the presence of the catalyst according to the invention.

FIELD OF THE INVENTION

The present invention relates in general to catalysis, and morespecifically to a catalyst containing titanium in bonded form,non-crystalline silicon dioxide and at least one crystalline silicatephase which has a zeolite structure, wherein the non-crystalline silicondioxide is applied to at least one of the crystalline silicate phaseswhich have a zeolite structure, and wherein at least one of thecrystalline silicate phases which have a zeolite structure containssilicon-carbon bonds with which non-hydrolytically separable organicgroups R are bonded to silicon.

BACKGROUND OF THE INVENTION

It is known from EP-A 0 100 119, EP-A 1 221 442, DE-A 199 54 322 andEP-A 0 904 151 that olefins can be reacted with hydrogen peroxide togive an epoxide when a purely inorganic titanium-containing zeolite isused as catalyst.

However, all these disclosed catalysts have the disadvantage that theoxidizing agent being used (hydrogen peroxide; ethyl- orisopropylbenzene hydroperoxide) decomposes to some extent on thesecatalysts. The consequences are epoxide yields, with respect to theoxidizing agent, of <100% and in some cases safety-engineering problemsdue to the formation of molecular oxygen as a decomposition product ofthe oxidizing agent.

Furthermore, all the disclosed catalysts have the disadvantage that theyprogressively lose their catalytic activity during the reaction.

The disclosure in WO 99/01445 keeps the desired minimum olefinconversion constant for a limited time by increasing the reactiontemperature and/or pressure. The technical limits, however, are veryrestricted due to the high epoxide reactivity. Even small increases intemperature can markedly reduce the epoxide selectivity. In industrialplants operating on the kiloton scale, small reductions in productselectivity can endanger economic viability.

EP-A 0 743 094 and EP-A 0 790 075 describe thermal regeneration,preferably with molecular oxygen. To achieve target temperatures of 200,better 550° C., in a few cases the catalyst has to be removed from thereactor. At least, it is a common factor in the disclosed regenerationprocesses that the epoxidation reaction has to be interrupted for theregeneration period.

Short catalyst operating lifetimes result in production losses duringthe regeneration phase or require a redundant, cost-intensive productionpathway. Thus, the development of new catalysts which can achieve highactivities with industrially interesting operating lifetimes and highselectivities is desirable.

EP-A 1 221 442 describes regeneration of the titanium zeolite catalystTS1 with aqueous hydrogen peroxide. The disclosure is characterized inparticular in that regeneration can be performed while the epoxidereaction is taking place in a continuous flow system that is in thepresence of olefin, methanol and aqueous hydrogen peroxide.

The mechanism of deactivation is not fully understood. Possibly, coatingof the catalytically active solid surfaces with organic molecules takesplace to such an extent that the active epoxidizing species is no longeravailable for the desired reaction.

DE-A 199 54 322 describes TS1 molded catalysts which are characterizedin that the extrudates are composed of TS1 powder and other materialsbased on SiO₂ for molding purposes. These extrudates, which thus containcrystalline and non-crystalline SiO₂ phases, are impregnated withaminopropyltrialkoxysilane and a base, and simultaneously a reagent tomodify the surface of the extrudate, and then calcined at 550° C. in astream of air until no more silicon-carbon bonds can be analyticallydetected. Although the purely inorganic molded catalysts obtained inthis way have the same catalytic activity as similar systems without anysilane surface treatment in a reaction step which follows TS1 synthesis,they have the tendency to generate slightly fewer secondary products. Inaddition the resistance of the strands of extrudate to lateral pressureis about 50% higher. The subsequent reaction of PO with water ormethanol to give propylene glycol and methoxypropanol respectively isobviously suppressed a little as compared with disclosed catalysts.

The data in the table given below demonstrate this:

without modification with modification methoxypropanol [ppm]: 3100-38001700-3200 propanediol [ppm]: 400-600 300-500

For an industrial process, the development of catalysts which achievelonger catalyst operating lifetimes along with still higher epoxideselectivities and epoxide productivities is desirable. Furthermore, itwould be desirable to waste less of the expensive oxidizing agent due todecomposition on the catalyst and for use during catalyst regeneration.

To prepare catalysts on an industrial scale (ton scale) the processsteps for catalyst preparation should be as reproducible and simple aspossible. In order to achieve an economically viable process, the costsof catalyst preparation should be very low.

SUMMARY OF THE INVENTION

Thus, the present invention provides new catalysts for industrialprocesses which have high activities and do not deactivate while at thesame time having excellent selectivities and causing as little loss aspossible of oxidizing agent due to decomposition on the catalyst.

The present invention also provides a process for preparing thesecatalysts.

The present invention further provides a technologically simple liquidphase process for the selective oxidation of hydrocarbons by hydrogenperoxide on these catalysts which leads to high yields and low costs dueto high activities, very high selectivities and industrially interestingcatalyst operating lifetimes.

The present invention provides an alternative catalyst for the directoxidation of hydrocarbons, which eliminates, to at least some extent,the disadvantages of known catalysts.

These and other advantages and benefits of the present invention will beapparent from the Detailed Description of the Invention herein below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described for purposes of illustrationand not limitation. Except in the operating examples, or where otherwiseindicated, all numbers expressing quantities, percentages and so forthin the specification are to be understood as being modified in allinstances by the term “about.”

The present invention provides a catalyst containing titanium inelemental or in bonded form, non-crystalline silicon dioxide and atleast one crystalline silicate phase which has a zeolite structure,wherein the non-crystalline silicon dioxide is applied to at least oneof the crystalline silicate phases which have a zeolite structure, andwherein at least one of the crystalline silicate phases which have azeolite structure contains silicon-carbon bonds with whichnon-hydrolytically separable organic groups R are bonded to silicon.Furthermore, the present invention provides a process for preparing thiscatalyst and a process for producing an epoxide from a compound whichcontains a carbon-carbon double bond (preferably from propene),comprising reaction of the compound which contains a carbon-carbondouble bond with hydrogen peroxide in the presence of the catalystaccording to the invention.

The crystalline silicate phase which has a zeolite structure and whichcontains silicon-carbon bonds, with which non-hydrolytically separableorganic groups R are bonded to silicon, is called an organic-inorganichybrid zeolite.

The organic groups R are preferably present in an amount of 0.01 to 5wt. %, more preferably 0.1 to 4 wt. % and most preferably 0.3 to 2 wt.%, with respect to the amount of crystalline silicate phases which havea zeolite structure and which contain silicon-carbon bonds with whichnon-hydrolytically separable organic groups R are bonded to silicon.

When preparing the catalyst according to the invention, calcination isperformed at a temperature of 100 to 550° C., more preferably 200 to450° C.

Thus, the present invention provides in particular compositionscontaining mainly the elements silicon, titanium, oxygen and carbon,wherein these compositions contain organic silicon-carbon bonds inaddition to purely inorganic constituents and, furthermore, thecompositions contain at least one crystalline phase in the oxide ofsilicon oxide with a zeolite structure. The crystalline systemsaccording to the invention, which contain both inorganic and alsoorganic constituents, homogeneously distributed, are called hybridsystems in the present document. The present disclosure details both thesynthesis of these hybrid compositions and also the use of these hybridcompositions as catalysts.

Zeolites are crystalline, microporous aluminosilicates, the crystallattices of which are built up from SiO₄ and AlO₄ tetrahedra. Thisstructure leads to extremely regularly shaped cavities or channels, thedimensions of which are of the same order of magnitude (0.3-1.5 nm) asthe dimensions of many molecules.

The use of aluminum-rich zeolites (A, X or Y) as hydrophilic adsorbentsis based on the high polarity which is produced by the presence ofaluminum in the lattice. A drop in the aluminum content, bydealumination or, if possible, by appropriate methods of synthesis,leads to a reduction in the polarity of the lattice and thus to anincreasingly hydrophobic character for the adsorbent. If the zeoliteZSM-5 is synthesized in the absence of aluminum, silicalite-1, amodification of SiO₂ and a typically hydrophobic adsorbent, is obtained.

The incorporation of titanium in the lattice of silicalite-1 increasesthe polarity again. This leads to an increase in the adsorption capacityfor water and to a decrease in the capacity for adsorbing non-polarsubstances (S. Mirajkar et al., J. Phys. Chem. 96, 3073/3079 (1992)).The hydrophobicity should thus decrease with increasing titaniumcontent. In addition, one should be able to differentiate whether thetitanium is incorporated in the lattice or is present as amorphous TiO₂because the latter does not have any effect on the polarity of thelattice.

The titanium atoms, tetrahedrally incorporated in the TS1 (preferably1.3 mol %), are the so-called active sites. From a catalytic point ofview, it would be desirable on the one hand to incorporate more titaniumspecies without forming amorphous TiO₂ (as a precipitate) in thesilicalite lattice, but on the other hand a catalyst system which is ashydrophobic as possible (achieved by the smallest possible proportion oftitanium) greatly increases the adsorption of propene, and above all thedesorption of PO, and thus reduces secondary reactions of PO with waterto give glycols on the active sites.

Surprisingly, the present invention succeeds in synthesizing a titaniumsilicalite which is characterized in that non-hydrolysable organicligands in the xTiO₂(1-x)SiO₂ network are homogeneously incorporated sothat the stable crystalline structure, with its regularly shapedcavities and channels, is largely retained. The homogeneousincorporation of non-hydrolysable organic ligands is preferablyperformed by integrating co-condensation agents with non-polarhydrocarbons in the polymer.

In the present document, catalysts according to the invention are calledhybrid titanium silicalites or hybrid TS1. Crystallinity is preferredfor catalysts according to the invention because the tetrahedraltitanium centers then remain stable and catalytically active under theconditions of epoxidation, in particular given the stability of acrystalline lattice.

Furthermore, it is surprising that organic ligands only slightly hinderthe forming process of the amorphous arrangement to give a crystallineZSM-5 structure.

Catalysts according to the invention are particularly characterized inthat the decomposition of hydrogen peroxide on these systems is greatlyreduced. In many cases, the stability of H₂O₂ in the presence of thehybrid TS1 increases by a factor of more than 1.5-2 as compared withconventional purely organic TS1.

Hybrid systems according to the invention with elevated hydrophobicityare especially useful for epoxidation reactions with hydrogen peroxidebecause hybrid TS1 according to the invention, with its reducedpolarity, is obviously targeted towards and precisely adapted to therequirements of the catalytic reaction. Experimentally, it candefinitely be demonstrated that the diffusion problems of the non-polarreactants (e.g. olefins such as propene) and the polar products (e.g.PO) are clearly minimized. The hydrophobic character also provides thematerial with additional stability towards water vapor, which furtherprolongs the catalyst lifetime.

The synthesis of TS1, first published in 1983 by Clerico (ENICHEM), issufficiently well-known to those skilled in the art.

Syntheses of the hybrid TS1 in accordance with the invention are basedboth on the one-step synthesis according to EP-B 0 904 151 and also onthe two-step synthesis according to P. Serrano/M. A. Uguina/R. vonGrieken/M. Camacho, Appl. catal., A 1995, 124(2), 391-408.

In the classical one-step synthesis, the template molecule(tetrapropylammonium hydroxide as a pattern) is used both forhydrolysis/condensation of the silicon and titanium precursors and alsoto form the ZSM-5 zeolite structure.

The two-step synthesis, also known as the impregnation method for thesynthesis of purely inorganic TS1, is divided into the following twosteps:

Step 1: Preparation of an amorphous SiO₂—TiO₂ sol-gel intermediateproduct (cogel) of silicon and titanium alkoxides (stable incorporationof Ti(IV)-O-Si species before the actual zeolite synthesis(heterocondensation). Step 2: Conversion of the amorphous cogel into azeolite structure by impregnating with a template (tetrapropylammoniumhydroxide) followed by hydrothermal synthesis (autoclave reaction).

The hybrid TS1 catalyst is described in the following.

Organic-inorganic hybrid materials, in the context of the invention,preferably contain at least one crystalline phase based on a hybridSiO₂/RSiO_(x).

With respect to crystalline silicon dioxide, the main constituent ofmaterials according to the invention, the hybrid systems preferablycontain between 0.1 and 4 mol % of titanium, more preferably between 0.5and 2 mol %, most preferably between 0.8 and 1.6 mol %.

The titanium is preferably present in oxidic form and is preferablyincorporated or linked chemically in the organic-inorganic hybridmaterial via Si—O—Ti bonds. Active catalysts of this type have only verysubordinate Ti—O—Ti domains.

In active catalysts, it is preferred that titanium is bonded to siliconvia heterosiloxane bonds.

With respect to crystalline silicon dioxide as the base component of theactive substance, hybrid systems preferably contain between 0.01 and 5mol % of non-hydrolysable organic ligands, more preferably between 0.05and 4 mol %, most preferably between 0.2 and 1.5 mol %. Thenon-hydrolysable organic ligands are preferably incorporated or linkedhomogeneously within the organic-inorganic hybrid material.

Homogeneous hybrid compositions according to the invention, containingsilicon, titanium and carbon atoms, in a special embodiment in the driedstate, can be described approximately by the following formula (I)(residues formed on the surface after modification and optionallyincompletely reacted groups are not taken into account here):(TiO₂)_(x)(SiO₂)_((1−x))/(TiO₂)_(y)(RSiO_(1.5))_((1−y))/M  (I)

In this formula (I), (TiO₂)_(x)(SiO₂)_((1−x)) represents purelyinorganic crystalline TS1 (MFI crystal structure) or TS2 (MEL crystalstructure) and (TiO₂)_(y)(RSiO_(1.5))_((1−y)) represents organicallymodified TS1 (hybrid TS1; as a result of the hybrid TS1 fraction, theentire molecular unit, comprising xTiO₂(1−x)SiO₂/xTiO₂(1−x)RySiO_(4−y),is referred to as hybrid TS1 in the present document).

M in formula (I) is a heteroatom which can be incorporated into themolecular unit in addition to titanium, preferably Sn, Fe, Al, Ge orcombinations thereof.

x and y in formula (I) represent the number of oxygen atoms requiredeffectively to saturate the valencies of Si and Ti.

The composition (I) given above can be varied over a wide range.

The specific surface area of the organic-inorganic hybrid materials isnot restricted at all. The specific surface area of catalysts in theattached examples is within the range 0.5-100 m²/g. Systems with smalleror larger surface areas, however, are also catalytically active.

Suitable precursor compounds for silicon, titanium and promoter centersare advantageously appropriate low molecular weight organic-inorganicmixed compounds which are suitable for the sol-gel process or acombination of corresponding inorganic and organic-inorganic mixedcompounds. Low molecular weight in the context of the invention meansmonomers or oligomers. Polymeric precursor compounds of silicon,titanium and promoters are also suitable provided they exhibitsufficient solubility.

Preferred solvents for the sol-gel process are alcohols such asisopropanol, butanol, ethanol, methanol or ketones such as acetone, andethers such as THF or tert.-butyl methyl ether.

Suitable starting materials are in particular all soluble silicon andtitanium compounds of the general formula (II) known to a person skilledin the art which can be used as starting materials for the correspondingoxides or hydroxides,[R_(x)M′(OR′)_(4−x)]  (II)wherein

M′ is chosen from silicon and titanium,

R and R′ may be identical or different and, independently, may be chosenfrom C₁-C₁₂-alkyl and C₆-C₁₂-aryl,

wherein

x=0,1,2,3 and

R′ may also be H.

In a particular embodiment of the organically modified silanes, one ormore hydrolyzable groups have been replaced by terminal and/or bridgedsaturated (e.g. CH₃, C₂H₅, C₃H₇, etc.) or unsaturated (e.g. C₂H₃, C₆H₅)R groups(s). Polyfunctional organosilanes, e.g. silanols and alkoxides,may also be used. Silanes, organically modified or not, can also bereacted in the presence of dialcohols or polyalcohols such as1,4-butanediol, to give organically modified polysiloxanes. Bridged Rgroups (alkylene groups) in the context of the invention are bridgedstructures such as chain-shaped, star-shaped (branched), cage-shaped orring-shaped structural elements.

To synthesize catalysts according to the invention, organically modifiedsilicon precursors in which the steric demands of the organic ligandsare relatively low, such as e.g. methyltrimethoxysilane,methyltriethoxysilane, methyltriactoxysilane, ethyltrimethoxysilane,ethyl-triethoxysilane or similar precursors, are preferred.

Instead of monomeric alkoxides, their condensation products may also beused. Compositions according to the invention can be used in anyphysical form for the oxidation reactions, e.g. milled powders,spherical particles, pellets, extrudates, granules.

In a preferred embodiment, the powdered crystalline hybrid TS1 systemsare converted into mechanically stable molded items. Molded items arethe preferred modification for filling fixed bed reactors such as e.g.tubular reactors. Molded items produced by solidifying shaping processesare sufficiently well known such as e.g. strand extrusion (e.g.extrudates with a diameter of 1-12 mm in accordance with EP-B 0 904 151or DE-A 199 54 322).

Up to 15 wt. % of binder (with respect to the total weight of calcinedor conditioned catalyst) is advantageously mixed with the hybrid TS1systems according to the invention for strand extrusion purposes.Silicon dioxide, amorphous or crystalline, as a fine powder or as Siprecursor compounds (e.g. tetraethoxysilane) is preferred as a non-polarbinder. Other binders, such as e.g. are described in EP-B 0 904 151, aresuitable provided they do not greatly increase the Lewis acidity of themolded item (Lewis centers can react with functional organic groups,e.g. epoxide functions, and produce secondary products in this way).

To make a dough-like mixture from the material according to theinvention, the binder and solvent, e.g. water, alcohol or mixturesthereof, auxiliary substances such as methylcellulose, as issufficiently well-known from the literature, may be used in smallamounts.

The proportion of auxiliary substances, with respect to the totalweight, should be preferably less than 5 wt. %, more preferably lessthan 2.5 wt. %, for materials according to the invention.

The titanium centers are described in the following.

Precursors for the titanium centers are not fixed. For example, titaniumalkoxides, titanium salts or organotitanium compounds may be used.

Although any salts of titanium, such as halides, nitrates andhydroxides, can be used, titanium alkoxides, e.g. the butoxide,isopropoxide, propoxide or ethoxide, are preferred.

Titanium derivatives such as tetraalkoxy titanates, with C₁-C₁₀ alkylgroups such as iso-butyl, tert-butyl, n-butyl, i-propyl, n-propyl ethyl,etc., or titanium alkoxy complexes such as are described in U.S. Pat.No. 6,090,961, e.g.(η5-tetramethyl-cyclopentadienyl)-3-tert-butyl-5-methyl-2-phenoxy)-dimethylsilyl-titanium-dimethoxidesor other organic titanium species such as titanyl acetylacetonate,Ti(OSiPh₃)₄, dicyclopentadienyltitanium dihalide, titanium dihalidedialkoxide, titanium halide trialkoxide, titanium siloxanes such as e.g.diethoxysiloxane-ethyl titanate copolymer (commercially available fromGelest Inc.) are preferably used. Chlorine is preferred as a halogensubstituent. Mixed alkoxides of titanium with other elements such ase.g. titanium triisopropoxide-tri-n-butyl stannoxide may also be used.The titanium precursor compounds may also be used in the presence ofcomplex-forming components such as e.g. acetylacetone or ethylacetoacetate.

To synthesize compositions according to the invention, tetraalkoxytitanates are preferably used as titanium precursors such as e.g. thosewith C₂-C₆ alkyl groups such as iso-butyl, tert-butyl, n-butyl,i-propyl, n-propyl, ethyl, are preferred.

Thermal activation is described in the following.

After hydrothermal synthesis compositions according to the invention arepreferably activated further by a thermal treatment at 100-500° C. in avariety of atmospheres such as air, nitrogen, hydrogen. The crystallinematerial according to the invention is preferably dried at 80-120° C.and then heated to 300-500° C. under an inert gas. In some cases it maybe advantageous to complete thermal activation at the targettemperature, 300-500° C., in an oxygen-containing atmosphere. Thecalcination temperature and time depend on the target content of organicligands in the system according to the invention. From 450° C. upwards,burning-off of the organic species, especially in an oxygen-containingatmosphere, takes place to a much larger extent.

Thermally activated (conditioned) hybrid compositions according to theinvention frequently exhibit a significantly higher catalytic activityfor epoxidation with hydrogen peroxide and a longer catalyst operatinglifetime than known purely inorganic TS1 catalysts:

Compositions according to the invention deactivate slowly with time.

Regeneration by washing with hydrogen peroxide solution is known forpurely inorganic TS1 systems (for example from EP-A 1 221 442).

Surprisingly, it was found that hybrid systems according to theinvention, despite the presence of homogeneously incorporated orappended organic components, can be fully regenerated by washing withhydrogen peroxide solutions (e.g. 3 to 40% strength H₂O₂-methanolsolution). This finding is all the more surprising because theoreticallythe organic ligands could also be oxidized by the oxidizing agenthydrogen peroxide. A continuous test trial of 500 hours of epoxidationwith hybrid TS1/regeneration of hybrid TS1 on a kilogram scale showed noloss of organic ligands at all (IR analysis of the hybrid TS1compositions; powder and molded item).

Thus, the composition according to the invention can be used with allhydrocarbons. The term hydrocarbons is understood to include unsaturatedor saturated hydrocarbons such as olefins or alkanes and these may alsocontain heteroatoms such as N, O, P, S or halogens. The organiccomponent to be oxidized can be acyclic, monocyclic, bicyclic orpolycyclic and can be monoolefinic, diolefinic or polyolefinic. In thecase of organic components with two or more double bonds, the doublebonds may be present in conjugated and non-conjugated positions.

Unsaturated hydrocarbons with 2 to 15, more preferably 2 to 10 carbonatoms are preferred, in particular ethene, propene, isobutylene,1-butene, 2-butene, cis-2-butene, trans-2-butene, 1,3-butadiene,pentene, 1-hexene, other hexenes, hexadiene, cyclohexene, benzene.

The process parameters are described in the following.

Hybrid TS1 catalysts are preferably used in liquid phase reactions forthe partial oxidation of hydrocarbons in the presence of hydrogenperoxide. Hybrid TS1 catalysts are also active in the gas phase.

The process parameters for the hydro-oxidation reaction in the liquidphase can be varied over a wide range.

HO catalysts according to the invention operate in particular attemperatures of 30 to 200° C., more preferably 40 to 80° C. and inparticular at 40 to 70° C.

For economic and structural apparatus reasons it is often advantageousto operate under elevated reaction pressures for liquid phase reactions.The heterogeneous catalysts according to the invention exhibitparticularly high catalytic activity in the pressure range fromatmospheric pressure to 70 bar. A pressure range of 2 to 35 bar is morepreferred, most preferably 5 to 30 bar.

The residence time may also be varied over a wide range. The residencetime is preferably <70 seconds. Hybrid TS1 molded catalysts exhibitparticularly high catalytic activities with good selectivities withresidence times <90 sec. Very short residence times, in the lower rangeof seconds (<40 seconds), are also provided by the present invention.

The feed composition is described in the following.

Hybrid TS1 catalysts are preferably used in liquid phase reactions forthe partial oxidation of hydrocarbons in the presence of hydrogenperoxide.

In this way, epoxides are obtained from olefins, ketones are obtainedfrom saturated secondary hydrocarbons, and alcohols are obtained fromsaturated tertiary hydrocarbons, preferably selectively.

The molar amounts of hydrocarbon used, with respect to the total numberof moles of hydrocarbon, diluent gas, hydrogen peroxide and solvent, andthe relative molar ratios of the components may be varied over a widerange. An excess of hydrocarbon is preferably used with respect to theoxygen used (on a molar basis). The hydrocarbon content is typicallygreater than 1 mol % and less than 80 mol %. Hydrocarbon contents in therange 4 to 90 mol % are more preferably used, most preferably in therange 8 to 70 mol %. The hydrocarbon contents may be in an amountranging between any combination of these values, inclusive of therecited values.

The oxygen may be used in a variety of forms such as molecular oxygen,air, nitrogen oxide, hydrogen peroxide. Molecular oxygen is preferred.

The molar proportion of oxygen, with respect to the total number ofmoles of hydrocarbon, oxygen, hydrogen and diluent gas, can be variedover a wide range. The oxygen is preferably used in a molar deficiencywith respect to the hydrocarbon. 1-30 vol. % of oxygen is preferablyused, more preferably 5-25 vol. % of oxygen.

In the absence of hydrogen, molded items according to the inventionexhibit only low activity and selectivity. Up to 180° C., theproductivity in the absence of hydrogen is generally low; attemperatures above 200° C., large amounts of carbon dioxide are formedin addition to partial oxidation products.

Any known source of hydrogen can be used, such as pure hydrogen, crackerhydrogen, synthesis gas or hydrogen from the dehydrogenation ofhydrocarbons and alcohols. In an embodiment of the invention, thehydrogen may also be produced in situ in a downstream reactor, e.g. bydehydrogenation of propane or isobutane or alcohols such as e.g.methanol or isobutanol. Hydrogen may also be introduced into thereaction system as a complex bonded species, e.g. a catalyst-hydrogencomplex.

The proportion by volume of hydrogen peroxide, with respect to the totalvolume, made up mainly of the components methanol/water/hydrogenperoxide/hydrocarbon, can be varied over a wide range. Typical hydrogenperoxide contents are 10-40 vol. %, more preferably 15-40 vol. %, mostpreferably 17-30 vol. %.

A diluent gas such as e.g. nitrogen, helium, argon, methane, carbondioxide, carbon monoxide or similar mainly inert gases, may optionallybe added to the essentially required reactant gases described above.Mixtures of the inert components described may also be used. Other inerthydrocarbons, such as for example fluorinated hydrocarbons(hexafluoroethane, CF₄, and others), may also be used as components todilute the feed gas or circulating gas. The added inert component isbeneficial to transportation of the heat being evolved in thisexothermic oxidation reaction and frequently for safety-engineeringreasons.

HO catalysts according to the invention have a large economic advantageover the prior art. Furthermore, systems according to the inventionexhibit a much longer catalyst lifetime than traditional purelyinorganic titanium silicalite catalysts.

Catalysts according to the invention can be prepared easily andcost-effectively from a chemical engineering point of view on anindustrial scale.

The present invention is explained in more detail by the followingexamples. The present invention is not restricted to these examples.

EXAMPLES

Instructions for Testing HO Molded Catalysts (Test Instructions)

A 250 ml BÜCHI glass autoclave was used under a semi-batch mode ofoperation, this having been conditioned using a thermostat (oil). Thereactor was provided continuously with feed gases using a set of twomass flow regulators (propene, nitrogen). For the reaction, 0.2 g ofhybrid TS1 powder catalyst, suspended in a methanol/water mixture (15 gof methanol, 5 g of 30% strength hydrogen peroxide solution in water),were initially introduced at 50° C. and 3 bar. A SWAGELOK pressureretention valve ensured that the pressure was kept constant. Thesuspension was stirred at 800 rpm using a magnetic stirring core. Thereactant gases were introduced directly into the suspension through a 1mm 0.2 mm capillary (immersion). The standard active substance loadingwas 21 l of gas/(g TS1*h). To perform the oxidation reaction with 0.2 gof TS1, the following stream of gas, referred to as the standard gascomposition in the following, was chosen: 0.252 l/h of C₃H₆, 3.96 l/h ofN₂ (corresponding to 6% propene in N₂).

For the sake of simplicity, in the following orientating trials only thePO vol. % concentration in the emerging stream of gas was detectedquantitatively using GC analysis; the amount of PO dissolved in theliquid phase was taken into account in a qualitative evaluation. (PO isthe abbreviation for propylene oxide).

The reaction gases were analyzed quantitatively using gaschromatography. Gas chromatographic separation of the individualreaction products was performed using a combined FID/WLD methodinvolving passage through three capillary columns.

FID: HP-INNOWax, 0.32 mm internal diameter, 60 m length, 0.25 μm layerthickness.

WLD: Sequential arrangement of

HP-Plot Q, 0.32 mm internal diameter, 30 m length, 20 μm layer thickness

HP-Plot molecular sieve 5 Å, 0.32 mm internal diameter, 30 m length, 12μm layer thickness.

The abbreviations are defined as follows:

FID: Flame ionization detector WLD: Thermal conductivity detectorHP-Plot Q: Gas chromatography column from Hewlett-Packard (fused silica;PLOT = porous layer open tubular) HP-Plot molecular Gas chromatographycolumn from Hewlett-Packard sieve 5 Å: (molecular sieve, 5 Angstrom;PLOT = porous layer open tubular)Synthesis of Hybrid TS1 by the Two-Step Process

The concentration of non-hydrolyzable organic ligands was 0.5 mol %,with respect to silicon dioxide.

The following substances were used as starting materials:

Si sources: Tetraethyl orthosilicate (TEOS, from Merck)Methyltrimethoxysilane (MTMS from Merck) Ti source: Tetrabutylorthotitanate (TBOT from Aldrich) Template: Tetrapropylammoniumhydroxide (TPAOH from SACHEN, HH) Water: Cation-free water (cations < 10ppm)

Reactants Amount used TEOS 137.78 g MTMS 0.46 g HCl, 0.05 mol/l 47.8 gTBOT 5.72 g Isopropanol 33.3 g TPAOH (base) 10-12 ml TPAOH (template) 32gHydrolysis of the Silicon Component

TEOS and MTMS were initially introduced into a 250 ml round-bottomedflask and stirred well, then the aqueous HCl solution was metered inover the course of 5 minutes and the mixture was stirred for about 1hour. A maximum temperature of 69° C. was reached after 39 minutes.After complete hydrolysis of the TEOS, the mixture was cooled to 1-2° C.in an ice bath; this process took about 40 minutes.

Incorporation of the Titanium Species in the Network

A solution of 5.72 g of TBOT, dissolved in 33.3 g of isopropanol, wasnow metered into the mixture very slowly, using a syringe pump. At arate of 11 ml/h, the metering process took 4.5 hours. Care was taken toensure that the temperature of the mixture did not rise above 3° C. andthat the mixture was stirred at maximum intensity because otherwise theprecipitation of anatase is favored. After completing addition of thetitanium component, the clear solution had to be stirred for a further 1hour under the same conditions in order to ensure complete condensationof the titanium species in the hybrid network. After that time, the freeTiOH groups were fully saturated with silicates so the reaction could beaccelerated without risk of the production of an anatase precipitate.The clear solution was then heated to room temperature (RT) over thecourse of 30 minutes.

Basic Gelling Process

About 10 ml of 20% strength TPAOH solution was metered into thewell-stirred mixture, using a syringe pump, at a rate of addition of 10ml/h. After 32 minutes, the gel point was reached. Over the course of afurther 10 minutes, the clear gel changed from a flexible structure to abrittle structure. After a further 60 minutes the gel material wascrushed in the mixer and then dried for 12 hours at 110° C. and under300 mbar pressure in a drying cabinet. The dried gel was then crushed to100-160 μm in a mortar.

Zeolite Formation

20 g of the dried and crushed powder were placed in an autoclave linedwith Teflon, intensively blended with 32 g of 20% strength TPAOHsolution (1.6 times the amount by weight) (the powder has to beuniformly wetted with liquid) and placed in a drying cabinet for 12hours at 170° C. under the naturally produced pressure (hydrothermalsynthesis). After cooling to RT, the contents of the reactor were rinsedout of the reactor with fully deionized water and the solid phase wasseparated from the liquid phase in a centrifuge (5 min, 3000 rpm). Thesolid was then washed three times with 30 ml of alkali-free fullydeionized water. After washing, the product was dried for 4 hours at110° C. and then conditioned and calcined in two variants:

Hybrid TS1 550: the dried amorphous hybrid gel was heated to 550° C. ina muffle furnace under a stream of N₂ (250 l/h) over the course of onehour. The product was then held at 550° C. for a further hour under astream of N₂ and then calcined at 550° C. for 15 hours with the supplyof air (100 l/h).

Hybrid TS1 400short: the dried amorphous hybrid gel was heated to 400°C. in a muffle furnace under a stream of N₂ (250 l/h) over the course ofone hour. The product was then held at 400° C. for a further hour undera stream of N₂ and then cacined at 400° C. for 15 hours with the supplyof air (100 l/h).

Hybrid TS1 400long: the dried amorphous hybrid gel was heated to 400° C.in a muffle furnace under a stream of N₂ (250 l/h) over the course ofone hour. The product was then held at 400° C. for a further hour undera stream of N₂ and then calcined at 400° C. for 30 hours with the supplyof air (100 l/h).

Example 1

For reaction, 0.2 g of hybrid TS1 550 powdered catalyst, suspended in amethanol/water mixture (15 g of methanol, 5 g of 30% strength hydrogenperoxide solution in water), were initially introduced at 50° C. and 3bar. The suspension was stirred at 800 rpm using a magnetic stirrercore. The reactant gases were introduced directly into the suspensionvia a 1 mm 0.2 mm capillary (immersion). To perform the oxidationreaction with 0.2 g of catalyst, 0.252 l/h of C₃H₆ and 3.96 l/h of N₂(corresponding to 6% propene in N₂) were bubbled into the liquid phase.

In a test performed in accordance with the test instructions, a constantPO selectivity of 95% was achieved. The PO concentration in the emerginggas phase was 5%. The rate of PO production remained the same until theH₂O₂ concentration in the liquid phase had dropped to below 4%.

Example 2

For reaction, 0.2 g of hybrid TS1 400short powdered catalyst, suspendedin a methanol/water mixture (15 g of methanol, 5 g of 30% strengthhydrogen peroxide solution in water), were initially introduced at 50°C. and 3 bar. The trial was performed in the same way as in example 1.

In a test performed in accordance with the test instructions, a constantPO selectivity of 95% was achieved. The PO concentration in the emerginggas phase was 6.1%. The rate of PO production remained the same untilthe H₂O₂ concentration in the liquid phase had dropped to below 4%.

Example 3

For reaction, 0.2 g of hybrid TS1 400long powdered catalyst, suspendedin a methanol/water mixture (15 g of methanol, 5 g of 30% strengthhydrogen peroxide solution in water), were initially introduced at 50°C. and 3 bar. The trial was performed in the same way as in example 1.

In a test performed in accordance with the test instructions, a constantPO selectivity of 95% was achieved. The PO concentration in the emerginggas phase was 6.5%. The rate of PO production remained the same untilthe H₂O₂ concentration in the liquid phase had dropped to below 4%.

Example 4

Cyclohexene was chosen instead of propene as an unsaturated hydrocarbon.A catalyst analogous to the one in example 3 was used for the partialoxidation of cyclohexene. Cyclohexene was continuously introduced intothe liquid phase with the aid of an evaporator.

In a test performed in accordance with the test instructions, a constantepoxide selectivity of 93% was achieved. The epoxide concentration inthe emerging gas phase was 4%. The rate of cyclohexene oxide productionremained the same until the H₂O₂ concentration in the liquid phase haddropped to below 5%.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A catalyst comprising: a) titanium in bonded form; b) non-crystallinesilicon dioxide; and c) at least one crystalline silicate phase having azeolite structure, wherein the non-crystalline silicon dioxide isapplied to at least one of the crystalline silicate phases having azeolite structure and at least the titanium atoms tetrahedrallyincorporated in one crystalline silicate phase, and wherein at least oneof the crystalline silicate phases having a zeolite structure containssilicon-carbon bonds binding non-hydrolytically separable organic groupsR to silicon.
 2. A catalyst according to claim 1 further comprising: d)additional silicon, in elemental or in bonded form, which is not presentin the form of non-crystalline silicon dioxide and is also not presentin the form of a crystalline silicate phase having a zeolite structure.3. The catalyst according to claim 1, wherein at least one of thecrystalline silicate phases having a zeolite structure has a zeolitestructure chosen from MFI, MEL, BEA, MOR and a mixed structure thereof.4. The catalyst according to claim 1, wherein the crystalline silicatephase having silicon-carbon bonds is an organically modified glass andcontains terminal and/or bridging organic groups in the crystallinenetwork.
 5. The catalyst according to claim 1, wherein the organicgroups R are present in an amount of about 0.01 to about 5 wt. %, withrespect to the amount of the crystalline silicate phases having azeolite structure and contain the silicon-carbon bonds with whichnon-hydrolytically separable organic groups R are bonded to silicon.